XR4Ti Archived Tech Articles
Engine and Auxillary System Sensor Guide - A guide for locating sensors for the engine and other auxillary systems on the XR4Ti. Note: this is an image heavy page with 18 images with a total size of approximately 1.02 megabytes. If some of the lower pictures on the page display an "x" in the picture placeholder, right click and select "show picture".
Post Date: Sat, 13 Mar 2004
I put together a series of images that will help you decipher
where the various sensors are located under the hood of an
XR4Ti. The pictures were taken from both my road car (as of
March 04) which is an 87.5 XR4Ti and the engine that came out
of my racer, an 87 XR. These XRs don't represent the total
collection of variations of the sensor locations (some auxillary
systems were changed in late 88 and 89 and some early cars had
slightly different componentry and arrangements).
Sorry this page isn't more pretty, but nothing beats raw,
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ECA (engine management computer) inputs:
PIP Sensor (profile ignition pickup) - hall-effect sensor for
communicating crankshaft/distributor position.
TFI - Thick Film Ignition (or Integrated) sensor, aka "ignition
TFI and knock sensor (located in two possible postions, the
second orientation puts it on the back side of the intake
Knock sensor in intake manifold.
TPS location (#1), ISC (Idle Speed Controller) location (#2),
engine coolant temperature sensor (#3) and EGR valve (#4).
This engine coolant temperature sensor is the one the ECA
Engine coolant temperature sensor again, shown as viewed from
the front, above the valve cover.
TPS, throttle position sensor shown as installed on the backside
of the thottle body.
VAM - Vane Air Meter, located under the airbox and surrounded by
the black mounting bracket. Wiring connector is visible between
the two coolant lines and the outlet of the VAM has the hose
going out to the left of the picture.
O2 sensor as located in the turbo outlet casting.
BAP - barometric pressure sensor (#1), starter solenoid (#2),
air door solenoid (#3).
BAP sensor tells the computer about the atmospheric pressure for
injecting the correct fuel mixture.
The air door solenoid controls flow of vacuum to the valve
that determines whether the air in the car recirculates or
feeds from the outside (it controls the "thunk" when you
switch between Recirc and O/S on the fan control switch, if
your system is working properly.
ECA (engine management computer) outputs:
BCS - boost control solenoid, for the regulation of boost
pressure. On the manual transmission setup, where the boost
was programmed to increase from 10 psi to about 15 psi at
approximately 4500 rpm (correct rpm?), this solenoid
handled the pressure increase.
As you can see, it is disconnected on this car.
EGR - exhaust gas recirculation valve, for the reintroduction
of exhaust gasses into the intake tract. It provides several
functions when operational:
- reduces ignition temps by adding inert gasses to the
combustion chamber (reduction of NOx in exhaust gas)
- effectively reduces engine displacement by using those inert
gasses to take up space in the cylinder, thereby increasing
It operates when the EGR control solenoid introduces vacuum
The EGR control solenoid, sends a vacuum signal to the EGR
valve when activated by the ECA (engine management computer).
The ignition coil (#1) and spout connector (#2).
The spout connector, when disconnect allows the base ignition
timing setting to be adjust (prevents the ECA from advancing
Temperature gauge sender, as located under the intake manifold.
Overboost switch, sets off overboost buzzer in overboost
Radiator fan switch (#1), as installed in the lower intake
manifold. Controls the radiator fan. Additionally, the
port where the temperature gauge sender is located is
Post Date: Sun, 14 Mar 2004
Here's a submission by Richard Curtis:
Published by Chris Anglin.